The present invention relates to extension ladders and more particularly to a novel rung lock assembly for releasably locking of preselected stations adjacent rungs of relatively slidable ladder sections.
It has been long known in the ladder arts to broadly use rung locks for adjusting extension ladders to a desired length. Attention is directed to the long since expired U.S. Pat. No. 369,084, issued to J. E. Smith on Aug. 30, 1887. This long expired patent teaches a "clutch lever or rung lock pivotally mounted on a ladder fly section to be manipulated by a rope and pulley assembly located on the outer rail face of the ladder base section to lockingly engage any one of several selected spaced rungs on the base section only of the ladder. To allow locking, the rope of the assembly which is tied off to the rung lock must be fully released at a selected stage of operation in a comparatively complex and a comparatively undependable operation. Attention further is directed to long since expired U.S. Pat. No. 437,395, issued to J. J. Flynn on Sep. 30, 1890, which teaches a complex guide and crank arrangement to move one ladder section relative an adjacent section with a unitary pair of spaced "dogs" or rung locks pivotally mounted on the fly section also to lockingly engage any one of several selected spaced rungs on the base section only of the ladder. Individual lips engageable against the rails of the fly section limit movement of the "dogs" or rung locks and a separate rope independent of the fly section moving crank rope, disposed intermediate the spaced rails of the base section is utilized to release the rung lock unitary pair of spaced "dogs". Long expired U.S Pat. No. 565,750, issued to B. A. Hill on Aug. 11, 1896, teaches what appears to be a rocker rung lock mounted on the base or fixed section of a ladder, the spaced fingers of the rung lock being actuated by a moving rope into and out of engagement only with rungs of the fly or sliding section of the ladder. The relatively moveable ladder sections appear to be movable directly by hand. U.S. Pat. No. 613,848, issued to F. S. Seagrave on Nov. 8, 1898 teaches a rung lock normally suspended intermediate to and out of engagement of the ladder rungs which when in locked rung position can be pulley operated out of such position to the normally disengaged position. The long since expired U.S. Pat. No. 802,017, issued to F. T. Newton on Oct. 17, 1905, which also appears to be movable directly by hand also includes a rope questionably actuated rung lock. In this patent, the rung lock is mounted on the fly section of the ladder with the tension of the rope acting as a spring to pivot or rock the lock into urged engagement with a rung on the base section. A latch pivotally suspended from the rung lock serves to prevent rung engagement during downward movement of the fly section. British patent No. 748,515 to C. W. Catless, published May 2, 1956, teaches a rung lock which is pivotally mounted on said base section which depends on gravity and a separate rope passing along an outside face of a ladder fly section and through the rung lock with the tension of the rope causing pivotal movement of the rung lock and movement of the fly section. Finally, U.S. Pat. No. 4,299,306, issued to H. G. Hawkins on Nov. 10, 1981, teaches a rung lock frame, a portion of which is similar in geometry to the present invention, but which overall structure operates in a different manner. In accordance with the rung lock assembly of the present invention, a structure is provided which is straightforward, efficient and economical to manufacture and assemble, which requires a minimum of operational parts and yet allows for the ready and efficient releasable rung locking and moving of relatively slidable telescoping ladder sections of an expansible ladder in an operating manner readily, efficiently and smoothly controlled with a minimum of steps and with a minimum of binding by a sole operator and user with a single comparatively non-interfering cable. In addition, the features of the present invention can be employed with extension ladders of more than two sections and which utilize rungs of various cross-sectional configurations. Moreover, the present invention provides for a readily operable rung lock assembly with its several parts confined within the limits of the spaced ladder rails without unnecessarily restricting movement of personnel in various positions of ladder use. In addition, the present invention provides a novel modification wherein a portion of the operating cable extends in longitudinal fashion between relatively slidable ladder sections and is connected to a pivotal rung lock frame to pivot such frame with applied force at a position substantially adjacent the longitudinally extending cable portion, and substantially in spaced lateral relation to the apex located pivot point for such rung lock frame, eliminating the need for a cable guide adjacent the pivoted rung lock frame.
Various other features of the present invention will become obvious to one skilled in the art upon reading the disclosure set forth herein.